At present, about a half of tooth loss is due to dental caries and tooth fractures, and it is known that removal of dental pulp greatly increases the possibility of tooth loss.
The average lifetime of teeth is said to be 57 years at present. To enable a person to chew with his/her own teeth throughout the lifetime, the lifetime of teeth needs to be prolonged by 20 years or more. Despite of “8020” Campaign (to keep 20 teeth or more until 80 years old), people now aged 80 keep about 8 teeth on average, and the number of remaining teeth of elderly people has hardly increased. Thus, dental caries treatment requires drastic improvement.
When dental pulp is removed (pulpectomy), its potential of reparative dentin formation and defense mechanism against infection are lost, and an alarm signal, i.e., a pain, is lost, thereby increasing the danger of enlarged dental caries. In addition, there are no perfect methods for the pulpectomy treatment, and leakage from a tooth crown part after pulpectomy and root canal filling might cause a periapical lesion, a vertical fracture, an aesthetic loss, and a postoperative pain.
In view of this background, it is very important in this unprecedented aging society not to casually perform pulpectomy but to develop a new treatment for dental caries and pulpitis by regeneration of dentin and dental pulp incorporating dental regenerative medicine technology in order to prolong the lifetime of teeth.
Regarding dentin regeneration, as cell therapy or gene therapy, proteins such as bone morphogenetic proteins (BMP) or genes are introduced into dental pulp stem cells/progenitor cells in vitro, to stimulate differentiation into odontoblasts in three-dimensional culture, and the odontoblasts are autologously transplanted on an amputated vital pulp together with its extracellular matrix. Thereby, a large amount of dentin is formed (see NON-PATENT DOCUMENTS 1 and 2).
However, in a case of pulpitis, it is necessary to regenerate dental pulp tissue as well as dentin.
The dental pulp tissues are very rich in blood vessels and nerves. The dental pulp has potential to heal spontaneously. Specifically, when being injured, chemotactic factors are locally released, and stem cells migrate from the periphery of blood vessels in the deeper part of the dental pulp to the injured site, proliferate and differentiate, leading to angiogenesis and reparative dentin formation. In particular, the vasculature of dental pulp is important for supplying nutrition and oxygen, serving as a conduit for metabolite waste, and homeostasis in the dental pulp. The dental pulp innervation plays an important role in adjusting a blood flow, a liquid flow into dentinal tubules, and the internal pressure of the dental pulp, regulating inflammation, being involved in angiogenesis and infiltration of immunocompetent cells or inflammatory cells, and contributes to homeostasis in the dental pulp and reinforcement of defense reaction of the dental pulp. Accordingly, in dentin/dental pulp regeneration, interaction between blood vessels and nerves, angiogenesis, and nerve regeneration need to be taken into consideration.
SP cells include CD31−/CD146−SP cells and CD31−/CD146+SP cells in a ratio of about 1:1. As compared to the CD31−/CD146+SP cells, the CD31−/CD146−SP cells significantly promote angiogenesis, nerve regeneration, and dental pulp regeneration, and significantly express CXCR4 mRNA, a chemokine receptor to stromal cell-derived factor-1 (SDF-1).
It is known that SDF-1 is secreted from a wounded portion of, for example, the skin, migration of human stem cells to SDF-1 depends on expression of CXCR4. The CXCR4 is also called a marker of stem cells, and embryonic stem cell-like cells are fractionated as CXCR4+/SSEA-4+/Oct-4+ from human cord blood (see NON-PATENT DOCUMENT 3).
As nerve stem cells, CXCR4+/SSEA-1+ cells which migrate to central nerves and have remarkable potential for nerve differentiation, are fractionated from a mouse fetal brain (see NON-PATENT DOCUMENT 4).
It is said that CXCR4-positive cells are pluripotent cells and CXCR4 can be used to fractionate stem and progenitor cells which have potential for differentiation into cells secreting insulin in human pancreata (see NON-PATENT DOCUMENT 5).
On the other hand, regarding dental pulp regeneration, it has been said to date that dental pulp in a tooth with incomplete apical closure is regenerated after extraction followed by root canal treatment and replantation. It is reported that even in the case of a tooth with an incomplete root having a periapical lesion, dental pulp-like tissues are regenerated in the following manner. After extraction of a tooth, the root canal is thoroughly enlarged and cleaned, and filled with blood clot to the cementodentinal junction so that the cavity is completely sealed with mineral trioxide aggregate (MTA).
It is also reported that dental pulp-like tissues in a canine healthy tooth with a complete apical closure are regenerated by pulpectomy after tooth extraction, cutting of the apical part or enlarging the apical area to 1.1 mm or more, followed by replantation and filling the root canal with blood clot (see NON-PATENT DOCUMENT 6).
Most of the above reports on the dental pulp regeneration in the root canal are directed to immature teeth with incomplete roots, and it has not been proved yet that regenerated tissues in the root canal are specific to dental pulp including blood vessels and nerves. In addition, in all the reports, enlargement and cleaning of the root canal are performed in vitro after temporary extraction of a tooth, and the root canal is then filled with blood clot after replantation of the tooth.